Night vision equipment is used for many industrial and military applications. For example, such equipment may be used for enhancing the night vision of aviators, for photographing astronomical bodies and for providing night vision to soldiers or sufferers of retinitis pigmentosa (night blindness). The equipment often incorporates an image intensifier that is used to amplify low intensity light or convert non-visible light into readily viewable images. One such image intensifier is an image intensifier tube.
An image intensifier tube typically includes a photocathode with for example, a gallium arsenide (GaAs) active layer and a microchannel plate (MCP) positioned within a vacuum housing. Visible and infrared energy, for example, may impinge upon the photocathode and be absorbed in the cathode active layer, thereby resulting in generation of electron/hole pairs. The generated electrons are then emitted into the vacuum cavity and amplified by the MCP.
More specifically, when electrons exit the photocathode, the electrons are accelerated toward an input surface of the MCP by a difference in potential between the input surface of the MCP and the photocathode of approximately 200 to 900 volts depending on the MCP to cathode spacing and MCP configuration (filmed or un-filmed). As the electrons bombard the input surface of the MCP, secondary electrons are generated within the MCP. That is, the MCP may generate several hundred electrons for each electron entering the input surface. The MCP is also subjected to a difference in potential between its input surface and its output surface that is typically about 700-1200 volts. This potential difference enables electron multiplication in the MCP.
As the multiplied electrons exit the MCP, the electrons are accelerated through the vacuum cavity toward a phosphor screen (or other anode surface) by yet another difference in potential between the phosphor screen and the output surface of the MCP. This latter potential may be on the order of approximately 4200-5400 volts.
A power supply is generally used to generate and provide the various potential differences noted above and to further provide control voltages for various components of the image intensifier tube. The power supply and intensifier tube are expected to operate under a variety of lighting conditions, including, e.g., relatively low light, relatively high light, and bright flashes. Configuring and controlling a power supply to handle all these conditions can be challenging.